It is well known to provide fire dampers in ductwork of heating and air-conditioning systems for the purpose of automatically closing such ductwork in the event of fire so to prevent the spread of such fire within such ductwork through a building. Such automatic fire dampers generally comprise a closure or shutter which is normally retained in an open position by a mechanical catch mechanism which is automatically released when the temperature reaches a predetermined value so as then to allow such a shutter to move into a closed position in which it closes the ductwork to prevent or at least delay the passage of fire therethrough.
Such thermally actuable fire dampers as heretofore known normally comprise latch plates for engaging their shutters when those shutters are moved into their closed positions, as on release of the catch mechanisms. Such latch plates serve positively to hold the shutters in their closed positions further to reduce the possibility of the passage of fire therepast.
The latch plates presently used in such automatically operable fire dampers are relatively complex in their construction and are, therefore, relatively expensive to manufacture. For example, it is presently customary to provide on such a latch plate a generally cylindrical member or boss about which a spool type tension spring is wound, such spring being terminally secured to the shutter of the damper and acting to move that shutter into its closed position on thermal release of the shutter-holding mechanism. Such cylindrical members or bosses are normally secured to known latch plates by a riveting operation which inevitably increases the costs of manufacturing such a latch plate.
Additionally, known latch plates for the aforesaid purposes are normally formed with a cam surface along which a leading edge of a shutter is guided during its movement into its closed position. Frequently, it is presently necessary to provide shutter-closing springs in fire dampers and which springs are relatively strong in their action and, therefore, relatively expensive, in order to ensure that there will be no restriction of movement of the shutter during its engagement with such cam surface before it reaches its fully closed position.
It is a principal object of this invention to provide a latch plate for use in an automatic, thermally actuable fire damper of the type hereinbefore described and which latch plate has a relatively simple construction and which can, therefore, be manufactured at a relatively low cost.
A further object of the present invention is to provide a latch plate for use in an automatic fire damper and which latch plate can be manufactured in a single metal stamping operation while still providing not only a cam surface for guiding a fire damper shutter into its closed position but also an anchorage for a spool type tension spring operative to urge such a shutter into its closed position.
A further objective is the provision of a fire damper assembly of smaller overall dimensions, and greater internal free area for air flow than known dampers, by the improvement of the damper blades and hinge mechanism.